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The Influence of Man-made Structures and Land-use on
the Behavior of Tsunami from the 2011 Great East Japan Earthquake:
Some Examples from the Pacific Coast of Tohoku and Hokkaido
Kazuomi HIRAKAWA1* and Tetsuya KOMATSU2
1

2

Professor Emeritus, Hokkaido University
Former Postdoctoral Researcher, Faculty of Environmental Earth Science, Hokkaido University*email: hkazu@ees.hokudai.ac.jp

Abstract
A drastic change in the behavior of the 2011 Tohoku earthquake tsunami at specific sites or on a local
scale was caused by changes in coastal setting, land uses for fisheries, large-scale river course changes, andcoastal construction works such as super embankments, jetty ports, dredged ports and types of breakwater
seawalls. Such phenomena could be identified along not only the coast of Tohoku close to the epicenter, butalso that of Hokkaido, relatively far from there. This report presents some remarkable examples of theinfluence of man-made structures and land-use on the site-specific to local tsunami behaviors along the
Pacific coast of Tohoku and Hokkaido from the geomorphological view, and must provide the information for
the adequate mitigation to future tsunami disasters and evacuation from them.
Key words: 2011 Tohoku earthquake tsunami, coastal construction, geomorphological setting,land-use change, site-specific tsunami behavior

1. Introduction
On March 11, 2011, a magnitude 9.0 earthquake
occurred off the Pacific coast of northeastern Japan(Tohoku) and generated a tsunami that struck along
2,000 km of the Pacific coast of Japan. The tsunami
reached the Pacific coast of Hokkaido, the northernmost
island of Japan, about one hour after the earthquake.
According to the data of the 2011 Tohoku Earthquake
Joint Survey Group (2011), the tsunami rose to a heightof more than 30 m in valleys along the Tohoku coast
close to the epicenter, and reached a height of approximately 20 m to flood more than 5 km inland along the
Sendai Plain. Even in Hokkaido, 300-600 km north fromthe epicenter, the tsunami inundated most parts of the
Pacific coast to heights of 2-4 m, but some spots to
5.5-6.7 m (Fig. 1).
From the viewpoint of disaster mitigation andevacuation it should be noted that the run-up behaviors ofthe 2011 Tohoku tsunami were probably sensitively
influenced by wave breaking and diffraction associatedwith not only physiographic coastal settings, but also
coastal land-use and/or location/arrangement of various
coastal construction works, as already pointed by Mori etal. (2011, 2012). It seems, however, that there have been
insufficient site-specific or local observations andinterpretations of such tsunami behaviors, especially
Global Environmental Research
18/2014: 19-26
printed in Japan

from a geomorphological point of view. Therefore, thisreport aims to introduce some remarkable examples of
the tsunami run-up behavior along the Pacific coast of
Tohoku and Hokkaido in terms of geomorphology, and to
propose its consideration as important to the planning for
mitigation and evacuation in future tsunami disasters.

2. Outline of Study Area and Methods
This report presents the tsunami run-up behaviors
observed in two areas (the lowermost reaches of theKitakami River and the town of Taro) on the Pacific coastof Tohoku and four areas (Asahihama, Tokachi Ohtsu,
the town of Erimo, and Cape Erimo) on that of Hokkaido.
Their localities are shown in Fig.1.
In the Tohoku region, we interpreted the tsunami
run-up behavior associated with large-scale landform
transformation (man-made river channels) and a super
embankment. For this purpose, we read not only topographic maps, but also referred to compiled data (e.g.,
Haraguchi & Iwamatsu, 2012) on the inundation area andrun-up height of the tsunami in the Tohoku region.
In the Hokkaido region, we focused on comparatively
site-specific tsunami run-up behaviors related to changes
in the coastal setting, land use, and coastal structures suchas jetty harbors, reclaimed land and tidal seawalls, based
on topographic map readings and field observations.
©2014 AIRIES

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Fig. 1 Inundation and run-up height of the 2011 Tohoku Earthquake (adapted from a figure on http://www.coastal.jp/
tsunami2011/; Accessed on 1 July 2011). Warm and cold colors represent inundation and run-up height, respectively.
Inundation and run-up height along the Pacific coast of Hokkaido were approximately 3-5 m.

Fieldwork was conducted along the Pacific coast of
Hokkaido, focusing on the Hidaka and Tokachi coasts
from March 17 to 19, one week after the earthquake, andApril 2 to 4. Through our fieldwork, we carefully
observed tsunami traces with special reference to coastal
construction works. Simultaneously, inundation height
and/or run-up height were measured from the extent ofdebris, reworked beach sediment and water marks byusing laser range finders. Measured heights were corrected for tidal elevation for a comparative investigation,although the relative (real time) height of the tsunami
inundation and run-up would be significant to the people
living in the individual areas or sites.

3. Observations and Descriptions
3.1 The New Kitakami River and the tragedy of
Okawa elementary school
Along the lowermost reaches of the Kitakami River
with the fourth largest drainage basin in Japan, a tragedy
happened at an elementary school. Seventy-four of 108
pupils and ten of 11 teachers at the school became victimsof the tsunami. The pupils were waiting on the school
grounds, while the teachers were discussing to where
they should evacuate. About 50 minutes after the earthquake, the tsunami attacked the pupils and teachers,
although the school was located at approximately 5 km
inland from the coast (Fig. 2). They seem not to haveconsidered their dangerous geomorphological situation,
as described below, because of the relatively long distance from the coast.
The main reason the tsunami violently intruded so far
inland, more than 15 km in this valley, can be attributed
to the geomorphological setting tied to landform development and the man-made river channel structure.
Through the Holocene transgression, this whole valley
had been inundated, developing a ria-inlet or strait (Ito,1999). Due to this, the valley floor, starting from the tidal
flat, consists of successional wetlands, the elevation ofwhich is only 0-2 m above sea level up to the approximately 15 km upstream from the present rivermouth. The man-made New Kitakami River channel wasconstructed, along with a riverside dike 5 m high from
1911 to 1934, using such characteristic lowland landforms. Here we should note that the New Kitakami Riverchannel with a width >500 m led to the violent, rapid
run-up of the 2011 tsunami far (approx. 14 km) into thevalley.
The residents, particularly the teachers, should have
known about such a dangerous geomorphological setting
and recent artificial changes to the river channel in orderto evacuate safely or mitigate damage from the tsunami
disaster. It must be stressed that understanding thedevelopment of local-scale landforms and land-use
changes like the New Kitakami River channel is a key
issue for disaster prevention.

The Influence of Man-made Structures and Land-use on the Behavior of Tsunamis

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Fig. 2 Overview map of the lowermost reaches of the Kitakami River (see Fig.1 for location). Red area shows the tsunamiinundated area derived from archived data for “Promotion of Disaster Prevention and Reconstruction from the 2011 Great
East Japan Earthquake,” City Bureau, Ministry of Land, Infrastructure, Transport and Tourism (MLITT). The base map wasconstructed using “Fundamental Geospatial Data” available from the Geospatial Information Authority of Japan, MLITT.

3.2 The super embankment of Taro town
Taro is a small town situated along a narrow lowland
in a bay, where a world famous “super embankment” hadbeen constructed. Residents of the town of Taro had frequently suffered from tsunami attacks, such as those of1896 Meiji-Sanriku and 1933 Showa-Sanriku earthquakes, and therefore began to construct a huge dike, the“super embankment,” after the 1933 tsunami on theirown initiative. What role did the super embankment playin the 2011 tsunami? What difference in tsunami inundation and run-up in this area was there between the
super embankment and the breakwater seawall constructed later from the 1960s to 1970s?
Figure 3 shows the embankment arrangement and theinundation and run-up heights of the 2011 tsunami atsome localities in and around the town. As shown in Fig.
3, the tsunami inundation and run-up heights were highlyvariable at individual sites within such a narrow area. We
can see that a tsunami with a height of 30 m or higher ran
up into the small valleys. Even in the area behind thebreakwater seawall constructed from the 1960s to 1970s,
which was severely destroyed by the 2011 tsunami, thetsunami maintained a run-up height of nearly 20 m. In
contrast to these areas, a tsunami with a relatively lower
inundation height of 10 m or even less could be found in
the residential area behind the super embankment.
Because the height of the super embankment is 10 m
above sea level, the tsunami appears not to have violently
attacked, but to have just completely inundated the pro-tected hinterland. Therefore there were no victims,
although people evacuated to the schools located in thesmall valleys at about 10 m above sea level.
The super embankment, which has a slope of 45
degrees on both sides of the cross section, was not
destroyed anywhere by the 2011 tsunami. The tsunami
appears to have smoothly overflowed the super embankment due to its structure and form with the 45 degree
angle. On the other hand, the damaged newer breakwater
seawall surrounding the fisheries port should haveworked to weaken the tsunami energy, although it
appears to have been comparatively easily constructedwith a thin, vertical structure. Here we can draw attention
to the aerial arrangement of seawalls, where the super
embankment seems to have more or less mitigated the2011 tsunami disaster in Taro, although the town was
severely damaged.
3.3 The fisheries port and coastal changes at
Asahihama
The 2011 tsunami behaved very variably from onesite to another in and around the port, depending oncoastal conditions, as indicated in Figs. 4B, C and D. In
this section, we first explain the coastal setting at
Asahihama in order to promote understanding of thevariability of tsunami behavior on the coast. Next, we
document the features of tsunami inundation and run-up
in the following three areas: the fisheries’ port and thebeaches northeast and southwest from the port.

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Fig. 3 Super embankment in the town Taro (see Fig.1 for location). The base map is derived from
Haraguchi and Iwamatsu (2012). Red and orange areas on the map indicate the tsunami-inundated
area. Numbers indicate the approximate height of tsunami inundation, which can be read from thebase map. Only numbers with asterisk show the run-up height, based on the observations of thisstudy. Note the difference in inundation height in the area bounded by the super embankment.

3.3.1 Coastal setting
At Asahihama in Hokkaido, the fisheries jetty portwith reclaimed land is protected by breakwater seawallsof 5 to 7 m high (Fig. 4). Such engineering works havebeen constructed since 1973 to the present. Due to theconstruction of the jetty port, the supply of drift sand/gravel associated with longshore currents to the beachhas been completely stopped on the north side of the port.
In contrast, this jetty port has worked to trap drift
sand/gravel on the beach on the south side of the port. As
a result, coastal erosion and accretion on both sides of theport has occurred notably since then (Fig. 4B), andcontinues at present.
In fact, the beach profile in the erosional reach has
been changed to present a narrower and steeper backshore zone. Furthermore, the backshore zone is alreadylacking at some sites, so that the run-up of waters frombreakers has begun to reach the sea cliff directly. Therefore, in the severely eroded reaches, sea cliffs with aheight of ~10 m have been protected by the seawall,
which is up to 5 m in height, and has a slope with an angleof 45 degrees, during the last ten years (Fig. 4C).
On the other hand, drift sand/gravel in the accretion
reaches has accumulated up to a height of 4.5-5 m, andhas newly formed a beach foreshore and backshore in
front of an upland, which has a sea cliff of ~5 m (Fig. 4B).
The height of the new beach has nearly reached that of
the former sea cliff, meaning that the sea and upland havebeen connected with a gentle slope.

3.3.2 Fisheries port
The tsunami inundation height indicated by watermarks on the walls of storage houses was 3.4 m onreclaimed land within the port protected by the breakwater seawall (a height of ~5 m) (Fig. 4B). Namely, thetsunami had not exceeded the breakwater seawall of theport. As a result, the fluctuation of the tsunami wasrecorded by several levels of watermarks, indicating a
repeated tsunami. This means that the inundation heightin the port appears to approximate the tsunami wave
height along the coast, like those measured by the tidegauge.
Just outside the port, however, a tsunami with a
run-up height of 5.8 m flowed over the breakwater seawall at 5.0 m and into the reclaimed area (Fig. 4B). This
place is a specific area behind the jetty port, where
accretion of beach drift due to circulating currents is
occurring. The foreshore has a large slope gradientcorresponding to beach gravel of cobble to boulders, andtherefore favored a higher run-up.
3.3.3 Beach northeast from the port
The beach northeast from the port is characterized byprogressive coastal erosion, which has occurred since
1973 (Fig. 4B). Our observation of this beach shows thatthe sudden change in tsunami run-up height coincides
with the engineered stretch. In the stretch of nonengineered beach where the foreshore and backshore had
been maintained sufficiently in front of the sea cliff ofThe Influence of Man-made Structures and Land-use on the Behavior of Tsunamis

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8-9 m

Fig. 4 Tsunami inundation and run-up influenced by coastal construction works and related changes in
the coastal environment at Asahihama, Hokkaido (see Fig.1 for location). (A) Topographic map.
Box shows location of (B). (B) Inundation and run-up heights in meters. Arrows show direction oftsunami inundation. Google Earth image used for the base map. (C) Cross section of engineering
works against coastal erosion. Black lines and “p” in (B) indicate engineered sea-cliff and the shot
point for Photo (D), respectively.

5 m height, the tsunami run-up height was 3-4 m and did
not extend inland. On the other hand, the tsunami ran up
the sea-cliff protection, which had an angle of 45 degrees,
and reached a height of 8-9 m above sea level (Figs. 4C
and D). This run-up height was about 2.5 times higher
than that of the non-engineered reach. This fact strongly
suggests that the tsunami run-up was site- specificallyenhanced by the disappearance or reduction of thebackshore. Therefore, it can be considered that suchsite-specific amplification of the tsunami run-up was
evidently related to changes in the coastal condition.
Particularly in this case, we should stress that the tsunami
easily and smoothly ran up a side-slope of 45 degrees,
which was there for sea cliff protection, like the tsunami
did at the super embankment in Taro, Tohoku.
3.3.4 Beach southwest from the port
The beach southwest from the port has accreted seaward since 1973 (Fig. 4B). Accreted beach sediment has
already reached the top of the breakwater seawall of theport (~5.0 m high). This means that the tsunami could

potentially run up such a new beach easily and flow into
the port. The actual tsunami ran up to a height of 4.5 m,i.e., an invasion of the port by the tsunami was barely
missed.
3.4 Tokachi Ohtsu
The tsunami inundation and run-up around theTokachi Ohtsu fisherie’s port differed between thedredged port and a roadside seawall (Figs. 5A and B).
The details are described below.
The dredged port had been constructed by excavatinga wetland which was geomorphologically identified as anabandoned river course and marsh behind a beach ridge.
The inundation height of the tsunami in the port was 4 m
based on a watermark on the wall of a structure. The
pattern of the tsunami inundation (Fig.5B) clearly indicates that the tsunami intruded inland according to theoriginal micro-landform of the dredged port. Namely, thetsunami run-up in this area appears to have been strongly
controlled by the former micro-geomorphic conditions.
One of the issues to be considered is that the evacuation

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Fig. 5 Tsunami inundation and run-up influenced by coastal construction works around Tokachi
Ohtsu Port (see Fig.1 for location). (A) Topographic map. (B) Inundation and run-up heights
in meters. Arrows: direction of tsunami inundation. Yellow line: road. Google Earth image
used for the base map. (C) Cross section of engineering works for roadside protection. Blacklines and “p” in (B) indicate the seawall and shot point for Photo (D), respectively.

route, which actually suffered from tsunami inundation,
bypass the periphery of the dredged port.
On the other hand, the run-up height of the tsunami at
the roadside seawall stretching southwestward from theport and village was 6.5 m, which was significantly
higher than that of 3.5-4 m within the port or on the beach.
Such an enhanced tsunami run-up was probably due tobank protection along the roadside against waves, as
shown in Figs. 5C and D. This means that coastal
construction changed the tsunami run-up site-specifically.
In terms of evacuation, it should be carefully consideredthat the road along the roadside seawall was inundated by
the tsunami.
3.5 Erimo town, Shin-hama
The tsunami run-up height around the port of the townof Erimo varied from the site to site (Fig. 6), probably asa result of the influence of the jetty port, the tide seawall
and the arrangement of tetrapods. The inundation heightand run-up height within the reclaimed lowland of theport marked 2.8-3.7 m (The 2011 Tohoku Earthquake
Tsunami Joint Survey Group, 2011; Okazaki & Tsunami
Survey Team of the Geological Survey of Hokkaido,2011), and 3.5-3.8 m (Fig. 6B), respectively. In comparison with this reclaimed land, a higher run-up height
reaching 5.5-6 m was identified outside the port to thesouth (Fig. 6B), due to the direction of tsunami propagation. Houses protected by a 3.5 m tidal seawall wereinundated (Fig. 6B). In addition, the tsunami ran up thesmall valley in this area to some degree, and then destroyed just one house and a small part of the seawall(Figs. 6B and C) by its drawback. Additionally, thehigher run-up of the tsunami seems to correspond to abreak between tetrapod mounds.
In summary, such an observation indicates that thetsunami inundation and run-up changed in accordancewith coastal construction works. Namely, the jetty system
structure of the port probably worked to trap and amplify
the tsunami to a very small extent. Simultaneously, thearrangement of tetrapod mounds likely influenced thetsunami run-up at the site scale.
3.6 Cape Erimo
Another characteristic tsunami run-up was recordedon the coast near the Cape Erimo Port as shown in Fig. 7.
A part of this beach is used as a sea tang (seaweed) drying

The Influence of Man-made Structures and Land-use on the Behavior of Tsunamis

25

Fig. 6 Tsunami inundation and run-up influenced by coastal construction works around Erimo
Town Port, Shin-hama (see Fig.1 for location). (A) Topographic map. Box shows location of(B). (B) Inundation and run-up heights in meters. The arrow shows the direction of tsunami
inundation. “p” in (B) indicates the shot point for Photo (C). Google Earth image used for thebase map of (B).

Fig. 7 Tsunami inundation and run-up height around Cape Erimo Port (see Fig.1 for location).
(A) Topographic map. Box shows the location of (B). (B) Inundation and run-up heights inmeters. Arrows show direction of tsunami run-up onto the sea tang drying ground. Google
Earth image used for the base map.

ground by local people. Due to this land use, no engineering works had been constructed there, apart from the jetty
port (Fig. 7).
The tsunami ran up over the whole seaweed drying
ground area that can be identified as the natural foreshoreand backshore with gentle slopes. The run-up height wasrecorded as ~6.5 m on the southern part of the coast, anddecreased toward the port to the north (Fig. 7B); in fact, it
was 4 m in the port. Such a pattern of the tsunami run-up
height and the arrangement of the port suggest apossibility that the jetty seawall of the port trapped thetsunami, which propagated from the southeast, and thencaused a site-specific amplification of tsunami run-up
south of the port. Therefore, when thinking about

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K. HIRAKAWA and T. KOMATSU

tsunami run-ups we should assume that the coastal
setting together with the specific land use for fisheries
can cause a difference in the tsunami run-up.

4. Remarks
It is well known that many factors affect local tsunami
behavior. The key issue in this report is to present someexamples concerning the violent behavior and drasticchanges in the 2011 Tohoku earthquake tsunami associated with human modification of the coastal setting in
Tohoku and Hokkaido.
As pointed out from the case of the man-made channel of the New Kitakami River in Tohoku (Fig. 2), an
understanding of the coastal setting tied with thedevelopment of local-scale landforms and land-use
change is critical for disaster prevention. Moreover, thecase of the town of Taro in Tohoku (Fig. 3) suggests thatthe relationship between the 2011 tsunami on a local orsite-specific scale and the arrangement and structure ofembankments must be analyzed for adequate evacuationand mitigation of future tsunamis.
On the Pacific coast of Hokkaido, far from the epicenter, the inundation and run-up height of the 2011 tsunami
was generally 2-4 meters (Fig. 1). As already described in
Sections 3.3-3.6, however, sudden higher values oftsunami inundation and run-up height ranging from
6 to 9 m could be identified at some specific sites (Figs. 4,
5, 6 and 7), where coastal engineering work had been
done. Therefore, the effectiveness of various engineered
coastal structures, including fisheries ports, must be
carefully discussed hereafter based on site-specificobservations and analysis of tsunami behavior. Without
such information, it is difficult to grasp the restricted
inundation and run-up of a tsunami in relation to fisheries
ports’ structures, land use, engineering works against
coastal erosion and so on. The direct influence of such
artificial roughness on a tsunami should be noted andconsidered to avoid dangerous situations in evacuationand mitigation.
We have to imagine the tsunami inundation andrun-up as described above, even when a moderate
tsunami occurs. This is because people near the Pacificcoast of Hokkaido only narrowly escaped severe damage
from the 2011 Tohoku tsunami, considering thesite-specific irregular height of tsunami inundation andrun-up related to human coastal modification.

References
Haraguchi,T. and A. Iwamatsu (2011) Higashinihon Daishinsai
Tsunami Shosai Chizu (Detailed Tsunami Maps of the Great
East Japan Earthquake), Tokyo, Kokon-Shoin. (in Japanese)
Ito, A. (1999) Geomorphic development of the Kitakami Riverlowland and Holocene relative sea-level change around Sendai
Bay, Northeastern Japan. The Science Reports of the Tohoku
University. 7th series, Geography, 49: 81-98.
Mori, N., T. Takahashi and H. Yanagisawa (2011) Survey of 2011
Tohoku earthquake tsunami inundation and run up. GeophysicalResearch Letters, 38: Loog14, doi:10.1029/2011GL049210.
Mori, N., T. Takahashi and The Tohoku Earthquake Tsunami Joint
Survey Group (2012) Nationwide post survey and analysis of the2011 Tohoku Earthquake Tsunami. Coastal Engineering Journal, doi:10.1142/S05785634 12500015.
Okazaki, T. and Tsunami Survey Team of the Geological Surveyof Hokkaido (2011) Survey on the 2011 off the Pacific coast of
Tohoku Earthquake Tsunami of March 11, 2011 on the Pacific
Coast in Hokkaido. Geological Survey of Hokkaido, 83: 1-15.
(in Japanese)
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Engineers, Series B 67 (1): 63-66.

Kazuomi HIRAKAWA
Kazuomi HIRAKAWA is a professor emeritus at
Hokkaido University. He has studied tsunami
sediments, particularly along the coast of
Hokkaido, since the 1990s, and has intensified his
research in association with the 2011 Tohoku
earthquake tsunami.

Tetsuya KOMATSU
Tetsuya KOMATSU is a former postdoctoral
researcher at the Faculty of Environmental Earth
Science, Hokkaido University, Japan. His major
fields of study are geomorphology and Quaternary
science.

(Received 17 February 2014, Accepted 4 April 2014)